Method of concentrating minerals



June 12, 1945.

l l.. J. ERcK METHOD OF CONCENTRATING MINERALS 4 Sheets-Sheet l AFiled Feb. 11, 1942 Indien/a?" yo( QM. MN A @n l Y Q x .n QQ xm n nmww N June 12, 1945. I., J. Rek 2,378,356

METHOD OF CONCENTRATING MINERALS Filed Feb. l1, 1942 4 Sheets-Sheet 2 4%' j Fffo June 12, 1945. l.. J. ERcK METHOD OF CONCENTRATING MINERALS Filed Feb. l1, 1942 y,

4 Sheets-Sheet 3 Zn/vena?" RQ @TAS QN l METHOD OF CONCENTRATING MINERALS Patented June 12, i945 I 2,378,356

UNITED STATES PATENT OFFICE :masso ME'rnon or coNcaNrnA'nNc MINERALS Louis J. Erck. Nashwauk, Minn., assignor to Mlncrals Benellciation, Incorporated, Joplin, Mo.. a t corporation of Delaware Application February 1.1, im, serial No. 430,342 s' claims.. w1. zii-zo) It is an object of this invention to provide a is insuiilcient to produce teetering of the mass. method for concentrating ilne ores and coal by The raw mineral or dewatered material from the use of relatively inexpensive equipment and the primary classifier` is fed to a main concenwith increased emciency and recovery as comtrating machine,-which may be a machineof the pared with known methods. 5 rotary spiral, classiiler type so altered as to per- A further object is to provide a continuous, mit the maintenance of a relatively dense andk low cost method for -concentrating certain fine large mass of the mineral in the trough adjacent materials, such, for example, as ores of minus to the Weir. In this machine the mass of mateone-quarter inch sizes and minerals generally rial is agitated in such manner as to work the or such character that they cannot be'concen- 1 coarser particles of the lighter fraction (princitrated economically or efficiently by methods in pally coarse silica in the case of iron ores) to `general use such as those involving flotation in the surface while continuously drawing oil the heavy density fluid. froth flotation or utilizing lighter and coarser fraction from the lower end log washers and other known equipment. of the trough and removing the concentrates or A particular object is to concentrate minerals u heavier fractionv from the upper end of the maof mixed sizes and densities by employing a pluchine. In ore concentration work, some tine ore rality of hydraulic concentration operations beis drawn off from the lower or weir end of the tween which operations an intermediate or midmachine with the coarse silica and it is desirable dlings product is withdrawn and treated to elimito recover this line fraction by subsequent treatnate or reduce a substantial amount of the 90 ment. To accomplish this,Ihave found that the coarser, low density material, the product oi' the coarse silica and -iine ore may be passed over a middiings treatment being further subjected to vibrating screen of suitable mesh to permit the classiilcation to separate the bulk of the line, low oversize to be wasted or further treated as heredensity constituents from the fine, high density inafter described and the undersize from the constituents. u screen, comprising principally ne ore, may be My preferred procedure is as follows: After returned either to the primary classifier or to determining the maximum size of the material the main concentrator to be subsequently recovto be treated, whether this material be ore or ered from the latter. A number of modifications coal. it is passed over a scalping screen for the of and additions to the foregoing basic procedure, removal of any fraction which may be coarser vl0. within the scope of my invention, are hereinafter than that to be treated and then the undersize described and claimed.

of this screen is fed to suitable apparatus for I'he present application is a continuation in removing the extremely fine, lighter fraction of part of my application serial No. 395,809, led the material and slimes. For the latter opera- May 29, 1941, for Method of concentrating mintion any of a number of standard hydraulic claserals."

sifiers may be employed. The line, low density In the accompanying drawings I have illusmaterial overflows or is drawn off from the matrated two distinct types of hydraulic machines chine together with a small fraction of they exwhich are suitable for use in my improved proctremely flneiron or other high density constit'- ess. uent. This tine product may be wasted or sub- 40 Referring to the drawings: sequently recovered, if recovery is commercially Figure 1 is a diagrammatic illustration of a practical. The bulk of fine, high density mateilow `sheet and apparatus, including a hydraulic rial, together with the coarse high density and concentrator of the screw type, for utilizing my coarse low density materials, are discharged from invention in the concentration of minerals;

the ilrst classifying machine and then` treated Figs. 2, 3 and 4 are sections taken respectively to separate much of the coarser low density maon the lines 2-2, 3-3 and l--I of Fig. 1; terial from the other constituents. For this Fig. 5 is a ilow sheet diagrammatially illustreatment I maintain in the concentrating aptrating a modification of the preferred process paratus a mass of mineral which is too dense to .wherein the overflow from the main concentrapermit classification depending on particle size 60 tor is passed through a grinding mill and the and I work the coarser particles of low `specific grinding mill product returned to the primary gravity to the surface of the mass by a combinaclassifier; .v

tion of mechanical agitation having an upward Fig; 6 is a diagrammatic illustration of a ilow component and upward percolation of water sheet and apparatus, including hydraulic mathrough the mass such that the hydraulic force 66 chines having inclined troughs and agitating and conveying mechanism of the reciprocating rake type;

Fig. 7 is a section taken on the line 1-1 of Fig. 6, and

Fig. 8 is a flow sheet diagram of an application of the invention to the cleaning of fine coal and providing for the recovery of pyrite therefrom.

Referring to Fig. 1, an ore feed conveyor is indicated by the numeral I6. This conveyor delivers the ore to a scalping screen |1 of such mesh as to eliminate sizes larger than those to be concentrated. In the case of iron ore, the process being particularly applicable to minus one-quarter inch sizes, a screen of the corresponding mesh is employed and the oversize is either wasted or treated by some other suitable method. The undersize material, together with sufficient water to cause it to flow is conveyed through a conduit I8 to the feed box I@ of the primary classifierindicated generally by the numeral 2li. This machine is of the conventional type having an inclined trough 2| in which a screw type conveyor 22 is continuously rotated to work the ore from the lower end to the upper end of the trough.` A pool of water 23 is maintained in the lower portion of the trough, this water being supplied with the ore and also through pipes 24 communicating with a so-called hutch tank 25 extending along the bottom of the trough and communicating therewith through perforations. This tank extends only from the ore feed box a short distance toward the upper end -of the trough 2|. A considerable quantity of water is caused to overflow a Weir 28 at the lower end of the trough and this water carries with it much of the ne sand and slimes which are washed from the ore. The overflow is discharged through a conduit 21.

The product of the primary classifier is carried up the trough 2| and is discharged through a conduit 28 to the feed box 29 of the main concentrator indicated by the numeral 30. The upper end section of the screw conveyor 22 has a dewatering effect on the ore and the latter is caused to ow through the conduit 28 by adding water from the pipe 3|. My improved concentrator 30 has an inclined trough 32 formed with an arcuate bottom and provided with a Weir 33 at its lower end over which the coarser silica, together with some fine ore, is discharged. A screw conveyor having spiral flights 34 and an axial shaft 35 extends longitudinally within the trough 32 from end to end thereof.- The pitch of the flights 34 is such as to gradually work the ore toward the upper end of the trough when the shaft 35 is driven in the appropriate direction. The flights 34V are of the ribbon type having ample openings around the shaft 35 for the passage of liquid toward the Weir 33. In operation, the shaft 35 is continuously rotated by an electric motor (not shown) which may be mounted near the normally upper end of the trough and connected by suitable speed reducing gearing to the upper end of said shaft.

Fixed at suitable intervals on the outer periphery of the flights 34 is a series of lifter bars 31 adapted to perform the important functions of loosening the mass of ore in the concentrator section of the machine and working the coarser tailings to the surface of the mass. 'I'hese bars 31 extend in parallel relation to each other substantially from the Weir 33 to the upper end of the main body of ore or other material to be concentrated. Extending along the bottom and side portions of the trough 32 is a hutch tank 38 for distributing water under pressure to the mass of material. This hutch tank is subdivided into separate compartments by partitions 39 extending across the trough and by a central partition 40 extending longitudinally, approximately along the center line of the machine (Figs. 2 and 3). Water supply pipes 4| severally communicate with the compartments of the hutch tank and each of these pipes has a valve 42 for controlling the flow of water supplied thereby. As indicated in Figs. 2 and 3, the hutch tank communicates with the interior of the trough at the bottom and sides thereof through a multiplicity of small perforations 43.l By this arrangement water is forced up through the' mass of material in the trough and is properly distributed and controlled so that the resulting percolation is too weak to prov duce teetering of the mass.

The'feed box 29 is preferably formed with a projection 28a extending obliquely downward and toward the Weir end of the trough, Fig. 1. This projection is in communication throughout its length with the interior of the trough so that the material fed to the machine is distributed and directed in a corresponding direction in the accumulated mass of mineral. An outlet opening 44 is formed in the bottom of the trough 32 near its upper end for the discharge of the concentrate or heavier fraction of the material into a chute 45 (Fig. 1).

The Weir 33 extends substantially horizontally 'from one side of the trough to approximately the center plane of the machine and is located at the side of the trough toward which the material is worked upward by the screw flights 34 and bars 31, as indicated in Fig. 2. A baille 46 extending in the plane of the weir prevents the stream with entrained material from passing directly out of the lower or launder side of the mass in the trough. The material which passes over the weir is caught in a receptacle 41 mounted on the outer end of the trough and is discharged through an outlet conduit 48 at the bottom of this receptacle. The machine is preferably provided with the con'- ventional Akins type mechanism for raising the screw conveyor out of the trough and for gradually lowering the `conveyor into the trough when the machine is started after a shut down with a mass of material in the trough, to thereby avoid overloads on the conveyor when starting.

To recover the fine ore from the overflow from the weir 33 'and receptacle 41, the overflow material is conveyed to a fine screen 49 (Fig. 1) of the vibrating type. The maximum particle size of the screen undersize should be approximately equal to the maximum particle size which is eliminated in the primary treatment step. Screen sizes from 28 to 48 openings to the inch inclusive are preferred for fine iron ore work. The oversize from the screen, comprising principally coarse silica,may be wasted and the undersize, principally fine iron ore, is fed to a sand pump 53 and returned thereby through a pipe 5| to the primary classifier feed conduit |8 to be further cleaned and finally recovered in the main concentrator.

Operation of the screw-type concentrator Details of operation for the concentration of iron ore of minus a quarter inch sizes are here set forth by way of example. This material is fed into the feed box 29 of the concentrator 3B, together with suflicient water to render the mass fluid. As the material `enters the trough 32 the heavier fractions including much of the coarse iron ore and some coarse silica, together with are started on surface of mosto! the nnerircn ore, settle immediately to the bottom of the trough at the feed point and their upward path by the4 screw flights "34. The intermediate grade material which is largely silica, together with some of the ilner'iron ore, is accumulated in the lower end portion cf the trough where it forms a dense mass. By proper adjustment oi' the rate of feed relative to the speed of operationof the conveyor shaft 35,'this mass is maintained to approximately the level of the top of the weir 33, and, as illustrated in Figs. 2 and 3 inclusive, it is continuously supplied with water from the hutch tank 38, the water entering the mass from the perforations 43 and rising to the surface.

As further'indicated in Figs. 2 to 4 inclusive, the mass of material, indicated by the numeral 52, is maintained at a somewhat higher elevation at the left side of the machine than at the right side duef to the rotation of the nights 34 and lifting bars'31 in the direction indicated. Along the'opposite side of the trough, a stream of water 53 flows toward the lower end of the machine and carries lwith it the larger particles of tailings together with some fine `iron re and some of the remaining fine low density material or sand. Such tailingsv are gradually and continuously worked to the surface of the mass both by the rising water and by the mechanical lifting action of therotating bars 31. A bed of ne material 54, largely fine, heavy ore, is maintained between the bottom of the trough and the conveyor flights 34. The stream of water 53 flowing down the side of 'the' trough washes the coarse silica from the the mass to the rear of the machine from lwhich it is discharged over theweir 33. The

. bulk of the heavier material is gradually worked up 'the incline of the trough out of the water and is dewatered by the upper section of the conveyor,

being finally discharged through the opening 44 -and chute 45. l

The'primary classifier contains, near the lower end, only a relatively small mass ofthe ore 55 andA a relatively largel body of water 56 which is continuously supplied so that it overflows the weir 26 carrying the slimes and iine silica to waste. in "accordance with conventional classifier practice; In order to maintain the relatively large mass of material inthe main concentrator for my continuous'pr'ocess, the primary classiiler must be considerably larger 'than the concentrator machine.

The density of the mass of iron ore and water inthe concentrating section of the machine should be maintained approximately within the limits'of l55% to r15% solids, depending on the structure of the ore, In this mass the force of percolatng water is insuiiicient to produce teetering and the solid particles are too densely crowded together to permit classification depending on particle size. This condition is obtained by controlling'the vrelative rates of feed and discharge the cross section through the point of feed to the rear end or weir., Considering the top surface of the mass, there is also what may be termed a. secondary concentrating zone extending from the cross section through the point of feed centrally of the trough and upwardly from such section. and a final or third zone extending approximately from the point of feed tc the upper end of the mass along the lower or launder side ot the mass over which the stream 53 flows.

From the foregoing it will be evident that I maintain in the concentrating machine a long sloping sorting column of ore from which the coarser silica or lighter wastematerial is removed notwithstanding the fact that the treated material is of various sizes as well as different specific gravities. Unlike the vertical column laboratory glass classifier process, it is unnecessary for the success of my process to have all ore and waste particles of approximately the same size. It is thus apparent that one of the advantageous features of my invention resides ln the economies resulting from obviating successive screening operations.'

Hydraulic classifiers having inclined troughs and reciprocating rake-type conveying mechanism may be employedin carrying out my invention, as indicated in Figs. 6 and 7. In this case ofthe material. by adjusting the valves control- ,f

ling the hutch water and by controlling the agiwhich the hutch water is supplied, these zones extending approximately two-thirds of the length ofthe trough. Tests during runs of my process vwitli""iron ore in the screwtype concentrator have lshown that concentration takes place gen. erally'in three more or less distinct zones, the

primary or rough vconcentration zone being the i 'l portion of the mass extending approximately from the product of the scalping screen I1 is fed through the conduit I8 to a feed box 51 extending across the top of -an inclined trough 53. A weir '59 is provided at the lower end of the trough 58 and an outlet chute at its upper end for the product. Water under pressure is supplied through hutch boxes 8i and perforations in the bottom of the trough in accordance with common practice.l Suitable reciprocating rake mechanism includes longitudinal bars 82 supporting a multiplicity of rake blades extending across thetrough. Rake operating mechanism of conventional reciprocating type, such as that ldescribed in expired Patent No. 1,156,543, patented October 12, 1915, to D. J. Nevill, may be provided. Such mechanism moves the rake supporting bars 62 in parallel relation to the bottom of the trough and up the incline during the forward stroke, then raises the bars and rake blades in an arc during the reverse stroke, at the end of which the blades are'lowered to position to start the next forward stroke. This movement carries the solid particles of mineral step by step up the incline of the trough'againstthe current of water owing towardrthe Weir with the result that the slimes and extremely ne, low density material or mineral is discharged'over the Weir and through a conduit Sil.

The' product of the primary classifier trough 58 is conveyed'to'the feed box 65 of a second machine for further classifying and concentrating treatment in a trough 66. This machine has rake supporting bars 61 and transversely extending rake blades 38 generally similar to those of the primary classifier and operated in a similar manner to work the material up the incline of the trough and discharge it through a chute 69. Otherwise the secondary machine differs in a number of respects from the primary clasisfler in order to adapt the secondary machine to separate the coarser, low density material from the coarse and fine, high density material. For this purpose hutch boxes 10 are extended along the bottom of the trough 66 toward the lower end and beneath thepool of water 1| which is maintained in the trough. A denser mass of material is maintained ln the secondary trough 63 than in the primary machine trough i8 but with the rake type of conveying mechanism it is impractical to maintain as deep and dense a mass as in a machine having the screw type of conveyor hereinbefore described.

A baille 12 extendsacross the trough near the Weir, the lower edge of the baille being submerged in the pool. As shown in Fis. 7, the barile 'l2 is adjustable vertically as well as horizontally or to and from the weir and is supported on a pair of brackets 13 attached by bolts 'Il to the upper edge of the trough, the brackets being adjustable along the upper edge of the trough. Each bracket 'I3 is connected to the baiiie J2 by. a bolt'15 adapted to be placed in any of .a vertical series of perforations 16 in the baille. The weir 11 is of the common adjustable type.

In the operation of the concentrator shown in Fig. 6 the material falls from the feed box 85 into the pool 1I which is supplied with water from the hutch boxes 10. A mass of the mineral too dense to permit classiflcationvdepending on particle size is maintained in the lower portion of the trough 66 and the water ows toward the baille 'l2 upon the surface of this mass carrying with it much of the coarser and lighter material so that the latter accumulates in a stratum near the Weir and at approximately the depth of the lower edge of the baille. vThe water `nowing under the baille carries this coarser and lighter material into the restricted space between the barile and weir 11 and thence over the weir. The baille 'l2 prevents the mass of nner and denser material from being carried over the weir with the coarser material. Some fine high and low density materi'al is carried over the weir with the coarser low density material and is discharged with the latter from a conduit 18 onto a vibrating screen 1B. The oversize from this screen may be wasted or ground and returned to the primary classiiier, as hereinafter described. The undersize material is collected from the screen and pumped through a conduit 80 which returns it to the feed box of the primary classifier. It will be understood that theproduct of the secondary classifier which is discharged from the chute 69 comprises largely the fine and coarse. high density material or concentrates of the heavier ores.

The flow sheet shown in Fig. illustrates a modication of the foregoing method of procedure which does not require the use of a screen to eliminate the coarse silica from the concentrator overflow. As indicated by the legends, the ore is fed to the primary classler which operates as hereinbefore described to eliminate iine silica and slimes or other ne, low density material. The product of the primary classier is continuously fed to the main concentrator as hereinbefore described and the product of the latter is the concentrate whereas the overflow, instead 'of being screened, is ground in a suitable mill, such as a ball or rod mill, to reduce the coarse silica to such a fine state that it may be eliminated in the primary classifier. The product of the grinding mill is pumped to the primary classier feed box.

Another important field for the use of my process is in the treatment of fine coal. The principles of operation above described may be applied to the treatment of coal to produce a satisfactorily clean coal product for use in stokers or after grinding as pulverized coal. Much of the ilner coal is wasted by"methods in general use which ordinarily employ notoriously inemcient jigs and produce a relatively high priced product.

The flow sheet shown in-Fig. 8 indicates how 75 my process may be used in the treatment' of coal and recovery of pyrite therefrom. In this case containing the bulk of the coal is fed to a vibrating'screen of suitable mesh. The oversize or coarserfraction from the screen is the marketable coal productL and the undersize, consisting of ne slate, pyrite and coal, is preferably pumped back into the primary classifier. To recover the pyrite from` the slatel the product of the main concentrator is fed to a secondary concentrator.

The heavier fraction comprising largely Dyrite is separated from the slate in the secondary concentrator which is operated as hereinbefore described in detail. The overflow from this secondary concentrator is conveyed to a vibrating screen of suitable mesh to allow the passage of the smaller material containing some coal and ne pyrite. Finally, the undersize material from the screen is pumped to the feed box of the main concentrator, as indicated, while the oversize from the screen, consisting largely of slate, is wasted.

It will be understood that my invention may be employed in the concentration of ores other than iron ore and to non-metallic minerals where there is a fairly wide spread in speciiic gravity between the desired concentrates and the desired rejects. In the treatment of non-metallic minerals, as in the case of coal, the concentrate is discharged from the concentrator over the weir and the waste or tailings are discharged from'the upper end of the trough. For non-ferrous ore treatment it is not necessary to produce a iinished concentrate since the end point is usually reached after a further rening process. such, for example, as oil flotation. With such rening processes my procedure may be used to advantage in discarding the bulk of the waste \material. Other modiilcations of the flow sheets herein described within the spirit of my invention may include the use of three or more concentrator machines and the recirculation of the overflow from one machine to the machine preceding it.

It will be evident that my process involves not only progressive classiiication and concentration in a plurality of operations, but also the treatment of a middlings product such as the coarser, low density material which has been separated in one of these operations, to either eliminate such material from the circuit or to reduce it to iiner sizes which may be recirculated or subjected to further classifying treatment. At least part of my middlings product, after screening or grinding, is returned to the circuit for further hydraulic classification treatment. All fine low density constituents of most minerals cannot be eliminated in my primary classifying step. Consequently, the material that is ordinarily fed to the main concentrator machine contains some ne low density constituents as well as coarse low density constituents and coarse and fine high density constituents. It will also be evident that with each of the several types of classifiers some of the iine low density material is discharged over the weir or through the elevated outlet together with the coarse low density material and some ne high density material.

- This invention has been used with marked success in concentrating iron ores from the present tailings basins which are made up of ore rejected from the former concentration operations and containing fine iron and porous iron of sizes and types of ore which are extremely dimcuit totreat in jigs or other conventional equipment. Fairly good recovery of high grade material has been obtained from material on which jigs show practically no recovery.

Having described my invention, what I claim as new and desire to protect by Letters Patent is:

l. kThe continuous ,method of concentrating mineral containing substantial quantities of particles of substantially all size ranges up to the maximum size oi the particles being treated and of high density and of lower vdensity which comprises subjecting the mineral to a hydraulic classification operation causing fine, low density material to be separated and leaving a product containing coarse, low density and both coarse and nne, high density material, subjecting this product to hydraulic concentration in a separate apparatus whereinla mass of said mineraltoo dense to permit classification depending on particle size is subjected to upward percolation of water havapparatus wherein a mass of said minerai too dense to permit classiication depending'on particle size is subjected to upward percolation of sufiicient quantity of the screen undersize material into the iirst classication operation to maintain the density of said mass inthe concentrating apparatus.

4. The continuous method of concentrating mineral containing substantial quantities of particles of substantially all size ranges upto the maximum size oi particles being treated and of high and low density which comprises subjecting the mineral to a hydraulic classification operation causing ne low density material to be separated leaving a product containing predominantly coarse low density andboth coarse and fine, high density material, subjecting this proding force insuiiicient to produce a teetering of the v mass and mechanical agitation causing localized lifting and releasing effects to separate coarse and fine, high density material from a product containing coarse low density material and iine high. density material, transforming said last mentioned productv into one substantially free from coarse low density material and reintroducing a sufiicient quantity of the transformed product into the ilrst classification operation to maintain the density of said mass in the concentrating apparatus.

2. The continuous method of concentrating mineral containing substantial quantities of particles of substantially all size ranges up to the maximum size of the particles being treated and of high and low density which comprises subjecting the mineral to a hydraulic classification operation causing i'lne, low density material to be separated leaving a product containing coarse, low

density and both coarse and fine, high density material, subjecting this product to hydraulic concentration in a separate apparatus wherein a mass of said mineral too dense to permit classificatlon depending on particle size is subjected to upward percolation of water having force insufficient to produce a teetering of themass and mechanical agitation causing 'localized lifting and releasing eiects to produce two products, one-of which is relatively rich in high density material and relatively poor in low density material, and the other of which is relatively rich in coarse low density material associated with high density material, -grinding the last mentioned product and reintroducing a suiiicient quantity of the l ground material into the irst classification operation to'maintain the density of said mass in the concentrating apparatus.

3. The continuous method of concentrating mineral containing substantial quantities ofparticles of substantially all size ranges up to the f maximum size of the particles being treated and -of high and low density which comprises subjecting the mineral to a hydraulic classification operation causing ne low density material to be separated and leaving a product containing predominantlycoarse low density and both coarse and ne high density material, subjecting this product to hydraulic concentration in a separate lifting and releasing effects to produce two products, one of which is relatively rich in highI density material and relatively poor in low density material, and the other of which is relatively rich in coarse low density material associated with iine high density material, subjecting the product which is relatively rich in high density material and relatively poor in low density material to further hydraulic concentration in a second apparatus wherein a mass of said mineral too dense to permit classification depending on particle size is subjected to upward percolation of water having force insuflicient to produce a teetering of the mass and mechanical agitation causing localized lifting and releasing eiects to produce two prodcoarse low density material and reintroducing at least a portion ofthe transformed material into the iirst concentration apparatus, processing the relatively coarse low density product of the first concentrating apparatus to produce a relatively ne product and reintroducing the last mentioned product into the rst classiiication operation.

5.v The method of concentrating ores of minus one-quarter inch mesh containing substantial quantities of particles of substantially all size ranges up to the maximum size of the particles being treated which comprises the steps of eliminating slimes and fine silica therefrom, then subjecting the residue of the oreto hydraulic concentration in a separate apparatus wherein a mass of the ore too dense to permit classification depending on particle size is subjected to upward percolation of water having insuiiicient force to produce teetering of the mass.

ticles'of tailings to the surface ot the mass. overflowing the coarser tailings and some une ore and water from thel apparatus, discharging the concentrated ore from the apparatus, recovering the iine particles of ore from the overllow tailings and returning a suilicient quantity o! the fine recovered ore to the nrst mentioned step of the process for the elimination o! iine silica therefrom and to maintainthe density otraid `rnasu in the concentrating apparatus.

6. The method of concentrating minus one-quarter inch mesh containing substantial quantitiesot particles oi/f'substantially all size ranges up to the maximum vsise of the particles being treated which comprises the steps of eliminating slimes and iin/e'v silica therefrom, then subjecting the residue of the orelto hydraulic concentration in a separate apparatus wherein a mass of the ore containing between 55% and 75% solids and too dense to permit classiiication depending on particle size is sub- Jected to upward percolation of water having insuilicient force to produce teetering of the mass and mechanical agitation causing localized lifting and releasing effects to work the coarser particles of tailings to the surface of the mass. overiiowing the coarser tailings and some fine ore and water from the apparatus, discharging the concentrated ore from the apparatus, re-

` covering the nne particles of ore from the overl ilow tailings and returning atleast a portion oi the fine, recovered ore to the concentrating apparatus.

7. The method described in claim 5 which includes the step of recovering the ilne ore particles from the tailings by passing the overilow iron ores of v ings of the particles of ore to be recovered and .v

envases material .overy a vibrating screen" of such ymesh as to allow the passage through the screen opento reject the Ycoarser tailings.

8. The method described in claim 6 which includes the step of recovering the fine 'particles of ore from the coarser tailings by screening, the mesh of the screen being not larger than twentyeight openings to the inch and the undersize oi' the screen being returned to the concentrating apparatus.

9.1The method of concentrating ores of minus one-quarter inch sizes containing substantial quantities of particles of substantially ali size ranges up to the maximum size of the particles being treated which comprises the steps of eliminating slimes and nne silica therefrom, then subjecting the ore to hydraulic concentration in a separate apparatus wherein a mass o! the ore too dense to permit classification depending on particle size is subjected to upward percolation of water having insuiiicient force to produce teetering of the mass and mechanical agitation causing localized lifting and'releasing eiects to work the coarser particles of tailings to the surface of the mass, overflowing the coarser tailings and some iine ore from lthe apparatus, continuously discharging an ore concentrate from the apparatus, grinding the overow material from the concentrating apparatus and recirculating a sufcient quantity of the ground material to the first step oi the process for the elimination of iine silica therefrom and to maintain the density of said mass in the concentrating apparatus.

LOUIS J. ERCK. 

